This proposal seeks to elucidate mechanisms of early development of the inner ear in the zebrafish, Danio redo. The inner ear arises from a simple thickening on the surface of the embryo termed the otic placode. Our recent studies have revealed mechanisms underlying induction of the otic placode, early patterning of the otic placode, and specification of sensory hair ceils. We will follow up on these studies. Induction and early patterning of the otic placode requires Fgf signaling, and it has been suggested that another factor, Wnt8, participates in this process. Using mis-expression and loss of function techniques, we will test the relative roles of Fgf3, Fgf8, Wnt8, and Wnt8b in these processes. We will also examine the role of Fgf signaling in subsequent differentiation of sensory hair cells. The earliest known markers of otic development are members of the Pax2/5/8 family of transcription factors, which we hypothesize help mediate induction by Fgf signaling. The epistatic relationships between pax and fgf functions will be examined. Finally, we will identify additional genes acting in these pathways by screening for second site mutations that enhance the ear defects caused by mutations in pax and fgf genes. These early developmental processes, and the genetic pathways controlling them, are highly conserved. Indeed, disruption of these processes can lead to deafness in humans. Therefore, achieving a fuller understanding of how the inner ear develops could eventually lead to effective medical interventions for human deafness or other disorders of the inner ear.